Apparatus for balancing rotors



27, 1943. o. E. EsvAu ETA; 2,243,458

l APPARATUS FOR BALANCING ROTORS .Original Filed June 12, ,1937 4 Sheets-Sheet 1 INVENToRs @L-HND E. Esi/A1.

CARL, H, FwscHE H :R ATroNEY V May 27, 1941- o. E. EsvAL Erm. 2243,45

A APPARATUS FOR BALANCING ROTORS original Fnd June 12, '1957 4 sheets-Skeet 2 May 27, 1941.

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APPARATUS LFOR BALANCING ROTORS 4 Sheets-Sheet 4 original Filed Jung 12. 1937 AMPLIFIER FILTER INvEIfIToRs i E @sx/51.32%, .f/60H5 Q THE/n ATI'RNEY Patented 4May 27;#1941 APPARATUS Eon BALANCTNG Boreas oriana n. Emi, Allendale, and carl A. minne, Leonie, N. J.. assigner: to Sperry Gyrolcope Company, Inc., BrooklymoN. Y., a corporation of New York Aiipllcsuon :wie 12, las-serial No, 141,816 Renewed January 17, 1940 (cl. isf-53) This invention relates, generally, to the balancu is claims.

ing of rotors and the invention has reference, more particularly, to a novel apparatus especially adapted for the speedy dynamic balancing of gyroscope rotors, ilywheels, etc., in production l work.

In our copending application Serial No. 91,444. filed July 18, 1936-, there is disclosed a novel bal- 'in a balancing frame that is arranged to pivot in a single correction plane extending at an end of the rotor perpendicular to therotor axis so that the vibration movement in that plane causes ancing apparatus adapted to receive the rotor rapidly detect and determine rotor unbalance with a minimum hazard to the finished rotor.

Still another object of the present invention is to employ electromagnetic pick-up'units providing very loose coupling between the rotor frame and the pick-up units proper, there beingno mechanical coupling between these parts,`where by the critical speed is greatly lowered, e., the speed where the vibratory displacement of the rotor frame becomes very large and the angle between the displacement vector and the unbalanced weight hanges rapidly with speed, thereno vibration in the system,V whereby vreadings of the amount of vibration taken at the other end 'or the rotor give true indications of the unbalanced moment in such other end. Such an apparatus has been found Aessential in the balanc The principal object of the present invention is to provide a novel apparatus especially suitable for. productionbalancing, the said apparatus lcniiprlsing certain improvements' and reilne` ments over the apparatus ofwour copending ap,

rotor trimnions while inserting rotors into and removing therfrom the apparatus, the said apparatus utilizing duplicate electromagnetic pick- Y up units together with twosets ofrrotor frame spring means, one picktup'llnit and means for changing the pivotal rotor frame support fromone correction plane tol the other at will, thegshifting of the support also lserving to automatically connect the properpiclbup Vunit I to the indicating circuit, whereby' unbalance at both ,ends oi' the rotor may be determined'upon j a single insertion of the rotor into the apparatus. A further'. oblect'o! this invention lies in the plication, whereby more rapid balancing is obl at lower spels than possible in the apparatus of our copending application.

-Other objects and advantages will become apparent from the specition, taken in connection with the accompanying drawings wherein one embodiment of the inventionis illustrated.

In the drawings:

Fig. 1 is a perspective view of the novel apparatus of the present invention, showing a rotor mounted therein for balancing.

Fig. 2 is a partialiplan view of the structure of Fig. 1.

Fig. 3 is a fragmentary, sectional view takenl along line 3 of Fig. 2, the springs in the correction'planes being both locked preparatory to lie-h ceiving a rotor in the apparatus for balancing.

Fig. 4 is a lschematic plan view of the cam arrangement used for shifting the rotor frame supporting springs.

Fig. 5 is a vertical sectional view of a portion of the apparatus of Fig. 1 and shows the apparatus positioned for pivoting the rotor in the upper correction plane, as when determining the unbalanced moment in the lowerl correction'plan'e.

Fig. 6 is a sectional view taken along line i-I v one spring nieans being located at each correc- 4 tion plane, together with manually operable cam n oLFlg. 8. 1

Fig. 'I is a schematic diagram of the apparatus and connected circuits.

f Fig. 8 is a schematic view, in pick-up unit, and f y Fig. 9 is a sectionalv view taken along lilie 0-9 Similar characters-of reference are used in all of the above iigures to indicate 'corresponding 'Ihe underlying theory of automat-ic balancingv embodied'in the apparatus of this'invention is based on the iactj that assuming a ilxedrotor provision of a novel balancing apparatus of the above character that is so constructed that skilled operators can manipulate the same to speed, the rotating deflection of the rotor-shaft, rotor casing, etc., has a fixed phase relation .to

,fthev disturbing force o'rvweight, the deection lbe ing apparentas vibration. The motion resulting..-

elevation, of the at each end of the rotor from dynamic unbalance of the rotor is approximately circular in a plane perpendicular to the rotor shaft. Thus, a particle at the end of the rotor axis moves in a circular .path and this motion has a definite phase or angular relation to the unbalanced weight of Y the rotor, so that should the dynamic unbalance at one end of the rotor be advanced by a certain angle, the particle on the gyro axis will be correspondingly advanced by the same angle in its circular path. Two indications are necessary in dynamically balancing an end of a rotor, one indication being the magnitude and the other the position of the unbalanced weight. The circular motion of the particle on the rotor axis provides In accordance with the present invention, a

novel ring type of electromagnetic pick-up unit or vibration instrument is employed, which has a very loose coupling with the rotor frame at the axis of the rotor, two of these pick-up units being employed, one at each end of the rotor, to generate voltages proportional to the amplitude at a desired frequency. With the rotor pivoted at onel correction plane extending at right angles to the rotor axis at one end of the rotor, the voltage generated inthe pick-up unit at the other end of the rotor is proportional to the moment of the unbalanced rotor. weight in the other correction plane, so that a'voltmeter connected to the output of the pick-up unit will therefore indicate directly the degree of dynamic unbalance at such other end of the rotor or correction plane. The electromagnetic pick-up unit is designed so as to be sensitive to vibration in only one plane, and hence it generates voltage as though the motion of the particle were vibrating across the diameter of its circular path. By having the unit turnable, the same can be positioned to generate voltage along any diameter of this path and the value of the voltage output of all positions is the of, whereby `the same is caused to buck or boost the photocell output so that the meter or oscillograph will show when the phase anglebetween the two outputs is either zero or 180. The

angular position of the pick-up unit to give this phase relation serves to determine the angular position `of the unbalanced weight with respect to' the'.l non-reecting or unpolished portion of I table or other support 2, which bedplate has upwardly and downwardly extending arms I, 4 provided with vertical slide bearings l, 5' for receiving vertical shafts O, I' provided with teeth and adapted to be raised and lowered to any position desired within limits by means of knobs 1, 'I' having pinions meshing'with the teeth of shafts 8, i'. I'hese shafts carry angularly stationary pointers l, l' cooperating with degree scales l,

.9 provided on annular flanges attached to indi- 4 cator discs III, III' turnably mounted on the shafts 6, 6'.'

pick-up units II, II', rpectively.

Since these pick-up units are. identical, only one of them, for example, the upper one, will be described in detail, reference being had in this connection to Figs. 5, 7, 8 and 9. This instrument comprises one or more permanent horseshoe magnets I2' provided with a central cylindrical depending pole I3 of soft iron on which is wound same. The phase relation between the voltages j To obtain a reference frequency voltage while' at the sametime avoiding any generator mechanically attached to the rotor, we employa photocell receiving light reflected from the rotor a coil Il. The horseshoe magnet I2 is adapted to cooperate with anl armature I5 having the form of a soft. iron ring that is arranged to be fixed upon the rotor frame I6. This armature I5 oscillates with the rotor axis under influencel ofv rotor unbalance, so that with the central pole It inserted through the apertured center of ring i5, as shown in the lowerl portion of Fig. 5, the ring or armature I5 is caused to move in an eccentric path around the pole I3 without actually contacting the latter, thereby varying the flux through the central pole I3 periodically andgenerating a voltage in the coil Il having a frequency corresponding to that of rotor speed.

Mechanically, the amature I5 is provided, with a hollow cylindrical portion I1 that is threaded into a vertically adjustable rotor' bearing housing I8 that-carries a ball bearing I9 for receiving andsupporting a rotor trunnion. The housing Il is slldably mounted in ahollow hub portion 2i being balanced, said r'otor having a part, such as a half, of the surface thereof highly polished -and the remainder not polished, a suitable light Ink performing the balancing operation, the

output volt e of the pick-up unit is phased against the o put voltage of the photocell as by use of a suitable meter or. cathode ray oscillograph. The phase of the pick-up unit output is l adjusted by changing the angular position thereof the rotor frame I6. A thumbscrew Il is threaded into the hub portion Il of the rotor frame I I for urging a block 22 against the bearing housing I l to thereby lock this housing in dsired vertically adjusted position within hub 2i. The

lower pick-up unit II' similarly has its armature I5 carried by a rotor bearing housing Il', having a ball bearing I9 and being vertically 'adjustable in the hollow hub portion 2i' of the rotor frame.l I

and a vertical connecting member 24 positioned inwardly of the outer ends of the members 2l,

Indicator discs III, I0' are connected to turn with electromagnetic ing spaced approximately 120 apart to provide a three point support for the rotor frame .I6 as will further appear. With a rotor 26 to be tested `mounted in the apparatus so that its trunnions are supported by ball bearings I6, I6', the springs 26, 26' are respectively substantially. on allevel with the ends of the rotor 26, whereby these springs lie in the upper and lower correction planes'of this rotor.

The rotor frame I6 is adapted to be selectively -supported at either correction plane at will through the action of the springs 26', 26' as controlled from a knob 36. This knob (see Fig. 6)

is positioned adjacent the outer ends of one pair of springs 26, 26' and is fixed on the upper end of a vertical cam shaft 3I turnably supported in a casing 26 provided on bedplate I and having cams 32 and 62' provided thereon operating in slots 36, 33' provided in radially reciprocable follower blocks 34, 34 movable in guides in casing 26. Knob 36 is connected through a lever-arm 35, link 36 anda lever arm 31 to also turn a cam shaft 3|' similar to cam shaft 3|. Likewise cam shaft 3I' is connected through lever arm 36, link 36" and lever arm 46' to turn a cam shaft 3I" also similar to cam shaft 3l. Thus, as knob 36 is turned to turneam shaft 3l, the similar cam.

shafts 3I' and 3|" are likewise turned.

'I'he radially reciprocable follower blocks 34, 34' actuated from cams 32, 32' on cam shafts 3i, 3| and 3i" carry springshackleblocks 36 36' to which are rigidly secured the outer end portions of leaf springs 26, 26', respectively, for supporting these springs so as to extend horizontally. Spring shackle blocks 36, 36' are shown as being independently adjustable with respect to their follower blocks 34, 34' by turning nuts 46 provided on studs 4| projecting from blocks 36, 36', which nuts engage in slots providedin follower blocks 34, 64'. Y

Thus, by turning knob 36, the cams 32, 32 are larly that the three upper springs 26 move together either radially outwardly or inwardly and moved radially outwardly, for example, `the apexes of slots 21' move to firmly engage the retion offknob 36, springs 26 and 26' both engage their respective studs 25 and 25',- as s hown in as enewn in' Fig. vs. In 'an intermediate pesi- I Fig. 3, thereby rmly supporting the rotor frame I6 at both ends and facilitating the insertion of a rotor into this frame and its removal'therefrom.

Since the rotor frame is supportedat all times f either by the upper or lower springs 26' and 26', or by both, the frame is always properly centered with respect to the pick-up units I I, I I' and cannot become accidentally displaced. v'I 'he upper and lower hub portions 2I and 2l' are cut away at 42, 42' to enable free passage of the rotor trunnions into andout ofthe rotor frame I6.-

'Ihe lower portion of cam shaft 3l carries a switch lever 43'for'operating a double pole, double throw switch 44 (see also Fig. 7) that serves to selectively connect electromagnetic pick-up units' II, II' to leads 45 of an indicating circuit,

which leads extend to the mixer and attenuator-- 46. Thus, when the'upper springs 26 are alone rotor frame I6, the upper pick-up I I is electricalvly connected by switch 66 to leads 45.

To obtain the desired reference voltage, a lamp "contained within a housing 46 is employed in commotion with a photocell 56.- The light from lamp 41 is directed, by use ofasuitable lens sysf tern, upon the underside ofthe rotor 26 mounted supporting the rotor frame I6, the lower vpick-up f II',J is electrically connected by switch 44 to leads 45, and when lower springs 26' alone support the' in frame I6, the reflected light from rotor 26 bei@ received by photocell 56. The intensity of the iight 41 may be varied at will as by turning the knob 46 in Fig. l, thereby adjusting the resistance 4 6 (see Figs. 1 and '7) in the supply of lamp 41. The under surface of the rotor 26 is'fpreferably partially polished so as to form a good reflecting surface, while the remainder of this under surface has little'or no reflecting ability.

" Thus, for example; half ofthe under surface of actuated to effect alimited radial movement of -H springs 26 and 26', the cams being lso set anguduced central portions of the studs 25', as shown in Fig. '1, to thereby firmly support the frame I6 'at its lower portion correspondingto the lower correction plane of the rotor. 'Ihe 'cams 32, 32' are so shaped and relatively positioned (see espelimit ei its travel. the lower set or springe ze' to the other limit of its travel, the springs 26 are at the outer limit of their movement for engag- Y ing studs 25 to support the rotorframe I6 while the springs 26' are at the inner limit of their movement and out of engagement cially Fig. 4) that withknob 36j 'turned to one are positioned at`the outer limit of their radial fmovement to support the rotor frame I6, the uprotor 26 may be polished and the other half provided witha dull surface, as by sand blasting. As the .rotor 26l turns, the output of photocell 56 is caused to change 'cyclically atrotor frequency, which is also the output frequency of the pick-up unitsIlandII'. e

The output of photocell .56 is connected by leads 5I to the mixer. and attenuator 46 of thef' indicating circuit. This equipment comprisesal transformer'52 having two primary windings connected, respectively, to leads 45 and l5I and a single secondary winding connected across a potentiometer 53. vLeads 54 connect the potentiometer 53 to a band pass filter 55, the output of' which may be connected by leads 56 to a suitablelinear thermionic amplifier-.51. Thefoutput of amplifier 51 is ,applied by leads 56 to an indicator,- such as a voltmeter 56', or a cathode ray osciliograph may be used in lieu of meter- 56.

In use, to insert a rotor into the apparatus for balancing, the knob 36 vis preferably turned to' itsintermediate position sothat springs 26, 26' both. engage their cooperating studs 25, 25', therevby firmly supporting both ends of rotor frame I6. i The rotor bearing housings I6, I6 are their moved apart, if necessary, by loosening screws 26, 26' so 'as to accommodatethe rotor 2 6 therebetween, the rotor then being inserted from the nions 6I entering through cut away portions 42.

front, as shown in Fig. 5, the rotor between members 2 3, 23 and the rotor trun- 'I'he housings I6, I6' are then moved toward each other so that trunnions 6ly are seated in bearings with snide u', 75 n, le', whereupon thumb screws zo, zo' are again tightened, the rotor being now free to turn with- 'in frame Il. Air nozzles 02, 63' are shown in spot on the lower rotor surface.

Figs. 2, 3 and 5 for controlling the speed of rotor 29, nozzle 62 serving to drive the rotor while 62' acts as a brake, suitable valve means (not shown) being employed for controlling the supply of air -from these nozzles.

All rotors of the same' ge provided with non-reflecting or dull po` ons'of identical angular extent, the remainder of the rotor surface contacted by the light beam being uniformly polished. The pick-up scales 9, 9' are initially so set angularly with respect to the Vrotor reflecting surface that when the unbalanced weights at the ends of the rotor coincide with a definite angular point of the rotor non-reflecting portion or black spot, such as an end or the center thereof, the zero reading of scales 9, 9 will coincide with pointers 8, 8'.

Thus, to obtain this initial setting, weights are placed upon the ends of rotor 29 in a common vertical plane extending through an end of the To set the scale 9 properly, the knob 30 is ilrst turned so as to pivot the frame I6 in the lower correction plane, i. e., with springs 26 supporting the rotor. With the rotor up to speed, the knob 1 is operated to move pick-up Il down so that its pole i3 enters the central opening of armature I 5, but without coil Il touching the amature.

as to indicate the pick-up voltage only. 'Ihe knob 1 is now turned to raise the pick-up I I out of cooperation with its armature il, and the lamp 41 is turned on and knob 4l adjusted so that meter il reads as before, showing that the outputs of the pick-up l I and photocell Il as supplied through the mixer and attenuator 52 are equal. The pick-up Il is now again lowered into cooperation, with its armature I5 and with lamp 41 turned on, the pickup II is angularly adjusted until the meter I9 reads zero, lindicating that the equal outputs of the pick-up and photocell are directly out of phase.

The annular iiange 65 of the indicator disc Il is now adjusted angularly so that the zero of scale l coincides with the pointer 8. This is accomplished by loosening screws M (see Fig. 5) and bodily turning flange II until the zero oft scale 9 thereon coincides with pointer 8. The scale 9' is now similarly set by pivoting the frame Ii in the upper correction plane, equalizing the output of photocell 50 with that of lower pick-up ll', adjusting pick-up Il' till meter Il reads zero and then adjusting scale to zero.

The apparatus is now set for balancingrotors To determine the unbalance of the rotor in its upper correction plane, the rotor to be balanced is placedin the frame II, the latter then plvoted in the lower correction plane by turning knob ll so that springs 1i' support this frame Il, the

' output of pick-up 1| is read on meter II with lamp 41 out, whereupon the pick-up ,Il is now raised and the mmp n lighted andits brightness varied by turning knob ll until the output of meter l! is the same as that previously produced by'the pick-up I I. This reading of meter l! cor- 're ponds to the magnitude of the unbalanced weight. The pick-up Il is now lowered and turned until the meter reads zero. The indication of scale 8 now gives the angular position of the unbalanced weight at the upper end of the .rotor with respect to the end of the non-reflectingportion of the rotor surface.

With. lamp 41 turned on, the meter 59 is now read so lower correction plane, the knob 3u is now turned i. e., so that the latter is pivoted in the upper.

correction plane. I'he pick-up Il' is elevated to cooperate with its armature I5' and the output of this pick-up is read on meter 58 with lamp 41 out. The indication of the meter corresponds to the magnitude of the unbalanced" weight. Pick-up Il' is now lowered andlamp 41 lighted and its brightness varied by use of knob I9 until the output of meter 59 is the same as when receiving the pick-up signal. 'I'he pick-up Il' is now again raised and turned until the meter reads zero, whereupon the reading of scale 9^ .gives the angular position of the unbalanced weight at the lower end of the rotor with respect to the end of the non-reflecting portion of the rotor surface.

The indicated amounts of material are now removed from the rotor ends as by drilling holes of proper depth at the proper respective positions. A calibration curve of drill depth against voltage readings of meter 58 may be used Ain this conl nection.

While it would be very advantageous to balance the rotor perfectly4 in one reading, this ordinarily cannot be done due tothe considerable magnitude of tha initial unbalance of an average rotor, therebyf/ necessitating two or three readings. cation must be reduced from the order of two millivolts reading of meter 59 down to less than ten microvolts, a ratio of 200 to 1. By adjusting the attenuator potentiometer 5i, the signal voltage range of meter I! is varied and this meter can be used full scale on minimum signal. Since the signal voltage may change in the ratio of 100 to 1 or more, changing ,of.the meter scale by use of potentiometer I3 is mandatory.

In use, apparatus of the present invention provides the extreme sensitivity required in balancing airplane instrument gyroscope rotors without depending upon super-keen perceptions in the operator. The speed of balancing is several times faster than that possible by methods heretofore used, employing highly skilled operators. Rejections due to defective rotor balancing are reduced from nearly 50% to zero because the apparatus of this invention, in largely removing4 the humanv element in making the measurements, obtains the same degree of accuracy on all units tested;

Although the apparatus has been shown as used for testing vrotors per se, if desired, rotors may be tested while in their own rotor frames. To accomplish this, the frame I6 is replaced by a suitable ring member having plug clamps for holding the rotor frame in place while testing.V The'armatures I5 in such case are adapted for removable attachment to therotor frames.

6d The band pass `filter 55 serves -to eliminate harmonics, that would otherwise cause meter Il to give an erroneous voltage reading in measuring magnitude and make it impossible to phase against the reference voltage for determining position. The reference signal also has a high harmonic which the filter 55 eliminates. 'I'he pick-up and reference voltages are combined or added together bythe mixer transformer 52 and then filtered by the filter 55, thereby precluding'the possibility of uncompensated ,phase shifts inltering. vIi? desired, a`stageof amplification maybe inserted ahead of the lter 55.

The ring type pick-up used in this invention, i. e., the pick-upg II and Il' employing ring L To determine the unbalance of the rotor in its. shaped armatures loosely coupled to the main In a typical case, the unbalance indii t Y straits zpart' of the pick-up units and without actual physical contact taking place between the parts, is a denite improvement over the phonograph type pick-up4 disclosed in our copending application. When using the phonograph type pick-up, dampingis considerable because the angular position of the displacement vvector is never independent of speed in the operating range. Thus, vat 200 R. P. S. a change o! 20 R. P. S. results in'a position change of the displacement vector of 2%/2 degrees. An even more serious difiiculty `of the electromagnetic pick-up is its relatively high critical speed, sometimes known as its resonant speed and is the speed where the vibratorydisplacement becomes very large and the angle between the displacement vector'and the disturbing force, i. e., unbalanced weight, changes very rapidly with changes in speed. This is caused partly'by the phenomenon of two resonances in series, one of which is the spring mounted frame and the other the natural -frequency of the magnetic pick-up that. is

mechanically connected tol the lframe by the needle.

By using the` pick-up units of this invention, fthe critical speed is greatly lowered, for example, from 115 cycles f or revolutions per signal to 40 cycles, thereby allowing satisfactory rotor operation at much lower speeds than possible with the phonograph type pick-up unit, and hence corwould be substituted for the ampliiier 51.- This integrating amplifier would serve to integrate what is asimcd is:

for pivoting. the rotor and its frame in one plane, means for measuring the vibration of said rotor in another plane without actually contacting said rotor orl its frame, said measuring means being adjustable for producing'a :voltage variable as' to phase, means for producing a reference voltage dependent on the speed of the rotor, and indicator means for comparing the phase positions of said voltages to determine the location of unbalance.

2. In an apparatus for `balancing rotors, means for pivoting the rotor and its frame inlone plane,

means for produchig an alternating E. M. F. serving as a measure of the magnitude of the unbalan'ce of said rotor in another plane without actually contacting said rotor or its frame, said measuring means being adjustable for varying the phase thereof, and means for producing a reference alternating E. M. F.responsive to the speed o! said rotor for comparison. in phase with that of said measuring means, whereby the location o such unbalance may be determined.

3. In an apparatus for balancing rotorsmeans forl receiving and pivotally supporting a rotor about an end thereof, means for-supplying a reference voltage dependent on the speed of said rotor,.an electromagnetic pick-up having aportion thereof carried by said supporting vmeans and another separate portion thereof adjustable v for phasing the output thereof against said or add up the voltage utput of the pick-up inl such a way as to supply meter 59 with a voltage dependent Aupon tlie amplitudel of displacement of the armature I5, which, in turn, is a function `of the rotor unbalance.

Also, in some instances it is desired to know the forces acting upon `the rotor beal'ingsldueV reference voltage, and an indicator responsive to said voltages.

4. In an apparatus for balancing rotors, means for receiving and for selectively pivotally support- 44ing a rotor at either of two points on' the spin axis thereof, said rotor being otherwise free to deflect transversely in any direction, vmeans for rotating the rotor, means for supplying an alternating E. M. F, of a frequency corresponding to the speed of the rotor, electromagnetic pickup means actuated by transverse deiiection of lsaid potor to produce alternating E. M. F.s selectively responsive to the displacement o'f the said rotor axis about either'of said two'pivot to -rotor unbalance, and since these forces are proportional tol acceleration of the unbalanced mass of the rotor, byemploying a differentiating #type of yamplifier instead of amplifier 51, then the velocity signal voltage received by this ampliiier from the pick-up is converted into an acceleration or secondA derivative with respect to time voltage of the pick-up armature l5 displacement. v

The filter serves to eliminate all frequencies except the desired rotor frequency corresponding .to that rotor speed at which it is desired to balance. It is obvious that the photocell ref erence voltage, when a maximum as indicated by meter 59, can be used as an indication. of

' correctrotor speed for purposes of test.

points due to unbalance, and indicating means arranged to be controlled in'response to-said E M. F.'s.

@5. In an apparatus for balancing rotors, means for supporting a rotor and its frame, means for 'supplying an alternating E. M. F. of a frequency corresponding to thespeed of the rotor; said supply means comprising a photocell vactivated by a beam of light reflected vf'rom the rotor having a portion of its surface of reflecting nature and'another portion of non-reiieoting nature,

electromagnetic means for coupling tb said rotor frame to produce an alternating E.` M. IF.' rea0 sponsive to the unbalance of the rotor, said elecl tromagnetic means-comprising. an amature car-v ried by said frame and voltage generating means disconnected from'said armature, and-indicating means arranged to be controlled in response to said' E. M. F.s, said voltage generating means being tunable t9' vary the phase of the nM. F.

As many changescouldbe made in the above construction and many apparently widely different embodiments of this invention could be it is intended that all matter contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

made without departing from the scope thereof, l

output thereof, whereby its output may be used to oppose the output of said photocell.

6. In an apparatus for-balancing rotors, means for rotatably supporting a rotor, an electromagnetic pick-up for coupling to said means adjacenten end of the -rotor to produce. an alternating E. lM. F. responsiveto rotor unbalance, said pick-up having 'a portion thereof turnable about the axis of the rotor to vary 'the phase o: I

l. In an apparatus for balancing rotors, means the output of said pick-up, means for supplying an alternating E. M. F. synchronous with thespeed of the rotor, an indicator, and a mixer for receiving and combining said E. M. F.'s for use in controlling said indicator.

7. In an apparatus for balancing rotors, means forrotatably supporting a rotor, an electromagnetic pick-up for coupling to said means adjacent an end of the rotor to produce an alternating E. M. F. responsive to rotor unbalance, said pick-up having a portion thereof carried by said supporting means and another portion thereof turnable about the axis `of the rotor to vary the phase of the output ofsaid pick-up, means for supplying an alternating E. M. F. synchronous with the speed of the rotor, means for combining said E. M. F.'s, a filter for receiving said combined E. M. F.s and acting to eliminate harmonics, and an indicator operable in response to the output of said filter.

8. In an apparatus for balancing rotors, a rotor frame adapted to receive a rotor, spring means for pivotally supporting said frame selectively about either of two correction planes extendine` perpendicular to the rotor axis, said rotor and supporting means being otherwise free to deflect transversely of the normal position of said axis in any direction, electromagnetic pickup umts associated with the ends of said rotor frame,V an indicating circuit including an indicator, means for supplying a `reference voltage to said indicating circuit. and switch means for selectively connecting said pick-up units -to said 'indicating circuit depending on the correction plane in which said frame is pivoted.

9. A rotor balancing apparatus as defined in claim 8, wherein said pick-up units are turnable to vary the phase of the output 'thereof for opposing said reference voltage, and angle indicators connected to said pick-ups for showing the angular position of the same when. the output thereof directly opposes said reference voltage, such angular position indication serving to determine the location of unbalance'in the rotor.

10. In an apparatus vfor balancing rotors, a frame adapted to receive a rotor and arranged tobe pivotally supported at a point on the spin axis of and adjacent an end of said rotor, an s electromagnetic pick-up loosely coupled to the other end of said frame concentric with said rotating axis for measuring the vibration thereat, means for supplying a'reference voltage, an

g for pivotally restraining said rotor at a point along the spin axis thereof, said axis being free to generate a cone haoving said point as an apex under the influence of unbalance, an electromagneticl pick-up having an armature carried by said supporting means and displaced therewith and cooperable magnetic pole-means independently supported out of contact with said armature, said pick-up serving to produce an alternating E. M. F. dependent on the velocity of vibration of said supportingmeans, means for producing a reference alternating E. M. F.-

dependent on the speed of said rotor, and indicating means for receiving said E. M. F.s and furnishing an indication of imbalance.

13. In an apparatus for balancing rotors of the type having parallel end faces, a rotor bearing frame adapted to rotatably support the rotor under test. means for pivoting said frame at a point on the spin axis of said rotor in the plane of one face of the rotor, said means being so constructed and arranged as to permit vibration of the rotor about said point as a pivot in any direction transverse to said spin axis, and means for measuring any such vibration of the other face of said rotor without actually contacting said frame. v

14. In an` apparatus for balancing rotors ot the type having parallel end faces, a rotor bearindicator circuit arranged for connection to Said pick-up and said reference voltage means, said circuit including an indicator for indicating and comparing the outputs of said pick-up and reference voltage means.

11. In an apparatus forbalancing rotors, a frame adapted to receive a rotor and arranged to be pivotally supported at a. point on the spin axis of and adjacent an end of said rotor, an electromagnetic pick-up loosely coupled to-the other end of said frame for measuring the vibration thereat, means for supplying a reference voltage, an indicator circuit having an input transformer provided'with primary windings arranged for connection respectively to said pickup and said-reference voltage supplylmeans, a. potentiometer connected to fthe output of said transformer, filtering and amplifying means supplied from said potentiometer, and an indicator operated from the output of said last named means.

12. In an apparatus for balancing rotors, means for rotatably supporting the rotor. means ing frame adapted to rotatably support the rotor under test for spinning about a vertical axis, means fon alternatively pivoting said frame at a point on said spin axis in the plane of either the upper or lower face of the rotor,l said means being so constructed and arranged as to permit vibration about said point as a pivot in any dlrection transverse to said spin axis, and means for measuring such vibration at the other face of said rotor without actuallycontacting said frame.

15. In an apparatus for balancing rotors of the type having parallel end faces, .bearing mem-l bers for temporarily rotatably mounting a rotor to' be tested, a common frame supporting said members, a plurality ot pairs of leaf springs symmetrically placed around! said frame and slidably secured to .said frame, each spring being thus secured at one point adjacent its inner end,

vthe two springs of each pair being placed substantially in the same planes as the two faces of the rotor, respectively, means for sliding all of the springs in one piane outwardly to clamp said frame in the plane of one'rotor face and means responsive to vibrations of the frame at the other rotor face for indicating the out of balance of the rotor at said face.

16. In an apparatus for balancing rotors of the type having parallel end faces, bearing members for temporarily rotatably mounting a rotor to be tested with its -spin axis vertical. a common frame supporting said members,l a plurality of pairs of leaf springs symmetrically placed around said frameandslidablysecured tosaid frame. each spring being thus secured at one point adjacent its inner end. the two springsof each pair being placed substantially in the same horisontal planes as the top and bottom faces of therotor, respectively, means for sliding all of the springs in one plane outwardly to clamp said frame in the plane of one rotor face and means responsive' to vibrations of the frame at the other rotor face for indicating they out 'or balance of 4the rotor at said face. I

17. An apparatus for balancing rotors as claimed in claim 15, in which said means for sliding .all of said springs in one plane outwardly, comprises a cam for each spring and a. linkage system connecting'the cams for all springs in one plane to move said springs equally and simultaneously.

18. In apparatus for lbalancing rotors, a frame adapted to receive a rotor and pivotally supported at a point on the rotor laxis adjacent an end of the rotor, said frame being otherwise unrestrained transversely of said axis, an electromagnetic pick-up comprising a stationary core, a coil mounted thereon, means for producing magnetic ux in said core and a ring-shaped armature mounted on said frame at an unrestrained point, said armature cooperating with said core without coming into contact therewith to vary the ilux in said core responsive to displacement oi said frame about said pivot point and thereby generate an E. M. F. in said coil proportional to roltor unbalance, and indicating means receiving said E. M. F. e

19. In an apparatus for balancing rotors of the typehaving parallel-end faces, a rotor bearing frame adapted to rotatably support the rotor under test, means for pivoting said frame at a point on the "spin axis of said rotor in the plane of one of said faces, said means being so constructed and arranged as to permit motion of said frame under the inuence of rotor unbalance in a substantially conical path having said point as an apex, a coil, means for producing magnetic flux linking with said coil, and permeable means mounted on said frame ata point other than said pivot point for varying the flux linked with said coil responsive to displacement of said frame from the position assumed when mounting a balanced rotor.

lORLAND E. ESVAL.

CARL A. FRISCHE. 

